Method and apparatus for code division switching of communication signals by trunk coding

ABSTRACT

A method provides for trunk group satellite switching using a code division multiple access (CDMA) scheme. The method includes receiving inbound satellite beams carrying individually encoded user signals including a plurality of inbound trunk groups, processing and mapping the trunk group elements to a plurality of outbound trunk groups, routing the outbound trunk groups to appropriate outbound satellite beams and transmitting the outbound beams based on common destination parameters. The trunk group switching allows for a reduction of on-board switching complexity, volume, and costs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a switching apparatus andmethod to be used in a communication switching system. It particularlyrelates to a trunk group switching technique to be used in a satellitecommunication switching system carrying wide-band signals that uses acode division multiple access (CDMA) scheme and a code division switchon-board the satellite.

2. Background Art

In typical satellite communication systems, the on-board switchingequipment primarily comprises a system which acts to receive and thenre-transmit user signals to an appropriate destination commonly referredto as a bent-pipe system. The satellite generally acts as a signal relaypoint to route user signals from a terrestrial origination to aterrestrial destination wherein all pertinent communication switching isperformed on the ground. To accomplish actual on-board switching for aplurality of user signals, the complexity of the satellite designquickly multiplies by requiring a digital receiver element for each usersignal (call). This hardware requirement greatly increases payload andlaunch costs, and may limit the number of users that can be supported bya satellite switching platform. The same need to limit equipment costand size may exist in other communication platforms (e.g., wireless,cellular, land mobile radio, etc).

There is a need to provide a seamless, flexible satellite communicationsystem that can provide desired user services with high performancewhile keeping satellite design complexity and equipment costs to aminimum.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for reducingsatellite on-board switching complexity to increase overall systemperformance in a wideband satellite communication system. The presentinvention overcomes the previously mentioned disadvantages by providinga trunk-coded satellite switching system wherein inbound satellite beamscarrying individually encoded user signals that are trunk-coded areadvantageously received, processed, and routed to appropriate outboundsatellite beams transmitted based on a mapping scheme. The trunk-codedswitching allows for a reduction of on-board switching complexity,volume, and costs. One embodiment of the present invention takesadvantage of orthogonal coding to perform trunk processing of inboundsatellite beams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the present invention showing arepresentative satellite communication system

FIG. 2 is a block diagram of an on-board switch in an embodiment of thepresent invention

FIG. 3 is a block diagram of originating customer premises equipment ina system according to an embodiment of the present invention

FIG. 4 is a block diagram of destination customer premises equipment ina system according to an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention discloses a method and apparatus for code divisionswitching of communication signals using a trunk-coded technique.Advantageously, the code division switching occurs in a satellitecommunication system environment wherein the switching occurs at aprocessing frequency using individually encoded user signals (narrowbanduser traffic codes and signals), wideband cover codes (e.g., psuedonoise or Gold codes), and trunk-coding (e.g., orthogonal Walsh orQuadratic Residue codes) to improve system performance. This processingfrequency may be any appropriate frequency enabling switching ofreceived satellite beams including, but not limited to an intermediatefrequency (IF), an analog frequency, or a digital baseband frequency.Gold codes change the properties of the signal by whitening the signalspectrum. Specifically, Gold codes make the signal spectrum more evenlydistributed in frequency so that it appears more like “white noise”.

The present invention of trunk coding enables switching at the processorfrequency therein making the plurality of access and modulation schemescreating the embedded narrowband user signals effectively transparent tothe satellite switch while still allowing groups of users (trunk-codegroups) to be switched efficiently. Alternative code division switchingtechniques are disclosed in U.S. Pat. Nos. 5,815,527 (Erving et al.) and5,878,037 (Sherman). U.S. Pat. No. 5,815,527 is herein incorporated byreference.

The trunk code provides sub-channeling within each beam to identifyblocks of users and associate the user with a particular outbound beam,preferably assigned at call setup, thereby reducing satellite on-boardswitching complexity. Preferably, the communication switching systemuses CDMA/spread spectrum modulated beams for inbound and outboundsatellite beams. Also, it is noted that particular non-critical aspectsof RF transmission and receiving processing are not described in greatdetail as they are not critical to the present invention and theseaspects are well-known in the relevant field of invention.

With reference to FIG. 1, a representative satellite communicationsystem 100 using the present invention is shown. The typicalcommunication path within system 100 include an inbound (uplink)communication path and outbound (downlink) communication path whereinthe inbound path comprises signals transmitted by ground users andreceived by communication satellite 150, and the outbound path comprisessignals transmitted by communication satellite 150 to ground users. Ascommonly operated within the system 100, communication satellite 150acts as a switching point to switch data signals received on a pluralityof inbound satellite beams to appropriate outbound satellite beams forsubsequent transmission. Satellite 150 includes an antenna systemdesigned to receive the plurality of inbound beams and transmit thecorresponding outbound beams wherein each inbound and outbound satellitebeam represent a different coverage area of the satellite communicationsystem 100. Typically, different coverage areas of the communicationsystem may overlap to ensure ubiquitous communication service.

Origination Customer Premises Equipment (CPE) 110 and 120 are shown as arepresentative sample of the plurality of origination CPE that may existwithin an actual satellite communication system. The CPE advantageouslyincludes a satellite dish for transmitting and receiving communicationsignals from an orbital satellite switching point. Typically, eachoriginating CPE will be located in a different satellite coverage area,although multiple CPE's may be located within the same coverage area. Ateach originating CPE located within a satellite coverage area, a userdata signal is modulated with a user code (narrowband usertraffic/spreading code), modulated with a trunk code, and then modulatedwith a beam code before conventional RF processing for inbound widebandsignal transmission to the satellite 150.

The user code helps identify a particular user signal, the trunk codehelps identify a group of individual user signals (a trunk group), andthe beam code helps associate a group of user signals with a particularinbound or outbound satellite beam and control interference fromadjacent beams. The wide-band trunk code (e.g., a CDMA waveform)isolates groups of users (trunks) from each other allowing theunderlying narrowband user code (e.g., waveform) to be transparent tothe receiving satellite. In a particular embodiment, this furtherenables the satellite to switch the inbound beams at a higher thanbaseband processing frequency (e.g., IF) and therefore never require thesatellite switch to decode the underlying access and modulation schemesused for the user signals.

Different trunk codes are used to encode the user signals of differentinbound trunk groups. The use of different trunk codes for differenttrunk groups uniquely identifies each user signal within that trunkgroup with a particular user. Each inbound beam may advantageouslyinclude a plurality of trunk groups to help facilitate on-boardsatellite switching. A set of trunks that share the same beam code wouldbe termed a beam group. The beam code typically is a short codecomprising two or four bits which doubles or quadruples the bandwidth ofthe signal. It is noted that use of a beam code is not a criticalelement to the present invention, and it's primary purpose is to helpcontrol interference between adjacent beams.

It is noted that although FIG. 1 shows a residential user, the presentinvention is not thus limited and can be applied to any satellitecommunication user (e.g., business or commercial user).

FIG. 2 represents a first preferred embodiment of the present inventionby showing a block diagram of the satellite on-board switch 300. Aplurality of inbound communication beams (310-1 to 310-N), transmittedby the originating CPEs, are received by the satellite receiver anddownconverted to a processing frequency (e.g., IF, analog, or digitalbaseband frequency) from the received radio frequency (RF) by thecorresponding plurality of downconverters (320-1 to 320-N). After theprocess of downconversion, the inbound beams are advantageouslyoverspread using mixer circuits (330-1 to 330-N). Over-spreadingincreases the bandwidth of the beam signal beyond the original bandwidthof the beam signal received by the satellite allowing multiple beamsignals to share the same communications line during further signalprocessing. The over-spreading codes are applied to the inbound beams toseparate the inbound beams for subsequent processing enabling the beamsto pass through the CDMA switch 300 without interfering with othersignals in the switch 300. This step of overspreading further allows forsubsequent separation of trunk groups from different beams. Theover-spreading code is preferably an orthogonal Walsh code, but can alsoinclude some other form of orthogonal or semi-orthogonal coding. When abeam code is employed, advantageously some beam groups can use the sameoverspreading code and still not interfere with each other. In thisimplementation, the group of beams sharing the same overspreading codewould be termed a switch group.

Following the process of over-spreading, the plurality of beams arecombined together in a summing circuit 340 forming a summation widebandsignal which carries all the information to be subsequently switched.Following summation, the combined signal is carried and distributed to aplurality of downlink trunk processors 350-1 to 350-N.

Each trunk processor includes a trunk switch 410-1 to 410L 410-N toisolate trunk processors 350-1 to 350-N which are inactive from thedownlink. Although two trunk switches are shown as closed in thediagram, one skilled in the art will appreciate that any number oftrunks may be dynamically selected at any time during on-boardprocessing to facilitate better system performance. As noted before,each inbound satellite beam includes a plurality of individually encodeduser signals carrying a user traffic code, a trunk code, and a beamcode. Correspondingly, each trunk processor includes processingequipment for decoding each particular aspect of the inbound beam exceptthe user traffic code. The trunk processor equipment includes a firstmixer to decode the overspreading code, a second mixer to decode thebeam code, a third mixer to decode the inbound trunk code, and a fourthmixer to apply an outbound trunk code. Although four mixers arepresently disclosed and shown in FIG. 2 for these communicationprocessing steps, those skilled in the art will appreciate that agreater or lesser number of mixers may be used to achieve the samefunction and results as four mixers. Advantageously, filtering (notshown) is applied after each mixing step.

With further reference to FIG. 2, the communication processing occurringon a selected trunk processor is disclosed. The signal carrying theinbound trunk group comes to a first mixer 360-1 to 360-N. The firstmixer 360-1 to 360-N applies a dispreading code, preferably a Walshcode, to the overspread beam group signal to recover the switch groupassociated with the trunk desired for processing. The processing ofdispreading returns the beam group signal to its original bandwidth asthe uplink beam group signal was received by the satellite which helpsprevent overlap of adjacent inbound beams and enables the satelliteswitch 300 to extract the necessary information needed to produce anoutbound satellite beam carrying outbound trunk groups. Following thestep of dispreading, a second mixer 370-1 to 370-N is used to remove(decode) the beam code to extract the beam group associated with thedesired trunk. Subsequently, a third mixer 380-1 to 380L 380-N is usedto remove (decode) the trunk code leaving the plurality of user signalsin the desired trunk. Following this step, for those inbound trunkgroups selected (the trunk switch is closed), a fourth mixer 390-1 to390-N is used to apply a second trunk code to the plurality of userssignals associating this group of users with a particular outbound trunkbased on a mapping established by a network switch controller (notshown) which is controlled by a network operations control center(“NOCC”). Advantageously, the second trunk code respreads the beamsignal (increases bandwidth from the underlying narrowband user signals)to isolate the outbound trunk group from other trunk groups (received onthe same uplink beam or other uplink beams) from other trunk groups thatmust share the same outbound beam. Once the inbound-to-outbound trunkgroup mapping is programmed into the network switch controller by theNOCC, the switching can be performed independently at the satellitesbased on the incoming beam including a plurality of trunk groups.Preferably, this independent switching to outbound trunk groups is basedon the trunk codes of inbound trunk groups.

This outbound trunk group is routed to a particular outbound beam pathand combined via a summer circuit 420 with other outbound trunk groupsto form an outbound beam group to be carried on the same outbound beam.Following this step of summation of the plurality of outbound trunkgroups on to a particular outbound beam, a second beam code is appliedusing a fifth mixer 430 based on the outbound beam path, and the beam isthen transmitted on the particular outbound path after conventional RFprocessing to a plurality of destination CPE's 200. In particularapplications, the interference suppression provided by a beam code maybe achieved by other means that include, but are not limited tofrequency division multiplexing, time division multiplexing, etc. Insuch applications, the beam group is transmitted without using a beamcode. Although not shown in FIG. 2, those skilled in the art willappreciate that conventional RF processing components such as filtersand amplifiers may be easily added to the on-board equipment but are notcritical to practicing the present invention. Also, although theon-board communication processing has been described using a singlesatellite transponder example, the above-mentioned processing can occurover a multiple number of transponders resulting in a plurality ofdifferent outbound satellite beams.

Generally, the communication switching system operations isadvantageously controlled using a terrestrial network operations controlcenter (NOCC). The NOCC, via the network switch controller, would assignparticular codes and dynamically (on demand) select the number andcomposition of particular inbound trunk groups for subsequent processingand outbound transmission. An asynchronous orderwire can be used atinitiation of user service to establish synchronization prior to issuinga narrowband traffic code. Also, the NOCC ensures that no two usersusing the same inbound or outbound signal beam and trunk code are usingthe same narrowband traffic code.

With reference to FIG. 3, the components of an originating CPE 500 areshown. An incoming data stream is modulated with a user code (e.g.,narrowband traffic channel code) using a modulator 510. The modulationtype may be any suitable technique including QPSK, BPSK, QAM, or directsequence spreading (CDMA). Also, the narrowband coding scheme caninclude a wide range of different coding techniques. In a preferredembodiment, the narrowband codes are narrow frequency traffic codes thatcorrespond to different narrowband Fast Fourier Transform (FFT) bins. Inalternative embodiments, other narrowband encoding techniques may beused including, but not limited to the following: wavelettransform-based approaches, sub-band approaches, and analog approaches.The narrowband coding ensures that one user's data is separable fromother user's data using the same trunk code when the transmission isreceived by the destination terminal on the downlink.

Following this step of narrowband coding, the user signal is modulatedwith a trunk code using a first mixer 520 creating a wideband signal.The trunk code may be any suitable coding technique including Walsh,Gold, direct sequence spreading, or another orthogonal orsemi-orthogonal coding technique. Subsequently, the user signal ismodulated with a beam code (cover code) using a second mixer 530 toassociate the user signal with a particular inbound satellite beam.Again, any suitable cover coding technique may be used (e.g., Goldcoding). A preferred embodiment uses direct sequence spreading codes(e.g., CDMA codes).

The beam code controls interference levels to and from other uplinkbeams. It may use orthogonal, semi-orthogonal, or psuedo-noise coding(among other coding techniques) to achieve this interference control. Apreferred embodiment uses short Walsh codes to orthogonalize theinterference from neighboring beams, and a psuedo-noise or gold code tocontrol the interference to/from beams which are farther away. Thepsuedo-noise or Gold code component would not increase the coding rate(bandwidth) of the signal, whereas the Walsh or orthogonal beam codecomponent would increase the rate.

Both mixers 520 and 530 operate at an IF range. After the beam code isapplied, conventional RF processing occurs wherein the signal isupconverted from IF to an RF range, filtered, amplified, andsubsequently transmitted to a satellite switching point on theparticular inbound satellite beam path. Amplification and RFtransmission are is performed using amplifier 540 and antenna 550respectively.

With reference to FIG. 4, the components of a destination CPE 600 areshown. Antenna 610 receives the outbound satellite communication beamcarrying a beam group code, trunk group code, and a plurality ofindividually encoded user signals. After the received beam signal isdownconverted from an RF frequency to a processing (e.g., baseband)frequency and passes through low noise amplifier 620, the beam code isremoved (decoded) helping to uniquely identify the particular receivedbeam using a first mixer 630. Those skilled in the art will appreciatethat an alternative embodiment could be implemented wherein the receivedRF signal is downconverted to IF instead of baseband for subsequentcommunication processing. Downconverting to baseband permits the use ofless complex and less expensive components for the processing of thereceived signal.

A second mixer 640 removes (decodes) the trunk code leaving theplurality of encoded user signals in the desired trunk group.Subsequently, a demodulator 650 demodulates the plurality of usersignals by applying a particular user code to filter out other usersignals and extract the desired original data stream carried by the RFcommunication signal. The demodulator uses a demodulation schemecorresponding to that used at the originating CPE (e.g., QPSK, BPSK,QAM, CDMA, etc).

As can be understood by those skilled in the art, the designation oforiginating and destination CPE are not rigid and these roles willcommonly be reversed back and forth in actual system operation whereininteractive communication is occurring.

Although the present invention has been described using a CDMA satellitecommunication system embodiment, it will be appreciated by those skilledin the art that modifications and changes may be made without departingfrom the spirit and scope of the present invention. As such, the methodand apparatus described herein may be equally applied to a wired,optical, or terrestrial wireless communication network.

What is claimed is:
 1. A method for simultaneous code division switchingof groups of individual signals, comprising receiving a plurality ofinbound communication beams at a communication switch, wherein each beamcarries a plurality of inbound trunk groups, and each inbound trunkgroup carries a plurality of individually encoded signals; processingeach inbound beam to a frequency for switch processing; combining saidprocessed beams into a summation signal; distributing each processedbeam, carried by said summation signal, to a different one of aplurality of trunk processors; decoding one of said plurality ofprocessed beams into at least one beam group and at least one trunkgroup, wherein said trunk group includes a plurality of individuallyencoded signals; applying a pre-determined trunk code to said pluralityof individually encoded signals included within said decoded trunk groupto obtain at least one outbound trunk group, wherein the trunk code isselected to isolate said outbound trunk group from any other outboundtrunk groups; generating an outbound communication beam including aplurality of outbound trunk groups, wherein said outbound trunk groupsare grouped based on a common destination parameter.
 2. The method ofclaim 1, further comprising: coding each inbound beam to allowcoexistence with other beams during the switch processing; and applyinga beam code to said outbound communication beam.
 3. The method of claim2, wherein: said step of coding includes applying an orthogonal code. 4.The method of claim 3, wherein: said orthogonal code is a Walsh code. 5.The method of claim 1, wherein: said step of distributing includesswitching at least one of said plurality of inbound trunk groups on to aparticular connection to generate said outbound communication beam. 6.An apparatus for simultaneous code division switching of groups ofindividual signals, comprising: a receiver for receiving a plurality ofinbound communication beams, each beam carrying a plurality ofindividually encoded signals including a plurality of inbound trunkgroups; a downconverter for downconverting each inbound beam to aprocessing frequency; a first mixer circuit for encoding saiddownconverted beams to reduce interference between said beams whencombined; a first summing circuit for combining said downconverted beamsinto a summation signal; a demultiplexer for separating said summationsignal into a plurality of inbound trunk groups; a second mixer circuitand a third mixer circuit for decoding one of said plurality of inboundtrunk groups into a plurality of individually encoded signals includinga first trunk group; a fourth mixer circuit for applying apre-determined trunk code to said plurality of individually encodedsignals to obtain an outbound trunk group; a second summing circuit forincluding said outbound trunk group in a plurality of outbound trunkgroups to obtain an outbound communication beam; and a transmitter fortransmitting said outbound communication beam, wherein said individuallyencoded signals are grouped into trunk groups based on a commondestination parameter.
 7. The apparatus of claim 6, wherein: saidplurality of individually encoded signals includes a beam group; andsaid apparatus includes a fifth mixer circuit for applying a beam codeto said outbound communication beam.